STATUS OF SWALLOWTAIL BUTTERFLY IN BRITAIN

Since the early 1950s, when the British swallowtail butterfly (Papilio machaon britannicus) became extinct at Wicken Fen, this subspecies has been confined to marshes around the Norfolk Broads, where its abundance appears to be declining. The ecology of the butterfly was studied in Norfolk and Wicken (by small scale introductions) and the main factors determining its abundance are described. A morphometric study of museum specimens showed that butterfly populations in Norfolk and Wicken differed in a number of size and shape characters. These differences were most marked between 1890-1920, but subsequently were almost lost. Studies of status and performance of the butterfly''s food plant, Peucedanum palustre, showed that it is smaller, produces less seed and is shorter-lived at Wicken than Norfolk. The possibility of successfully reestablishing the butterfly at Wicken, and the possible causes of the decline of the species in Norfolk are discussed.